The first change is often fluid, not “toxins”
When you sharply cut food intake, your body draws on glycogen—the stored form of carbohydrate in the liver and muscles. Glycogen is stored with water, so using it can make the scale drop quickly, mostly through water loss rather than a comparable loss of body fat. Eating less solid food also means less material moving through the digestive tract.
Juice supplies water and carbohydrate, but usually much less protein and fat than meals do. Depending on the juices and how much you drink, your overall calorie intake may fall substantially. Your body still needs energy, so it uses stored fuel; three days is not a special period in which the body switches on a unique cleansing process.
Your organs keep doing the filtering
The liver processes substances absorbed from food and other sources, while the kidneys filter the blood and remove many waste products in urine. These systems continue working during a cleanse. Juice does not pull a general store of toxins out of the body, and a three-day juice regimen does not replace the liver or kidneys’ ordinary work.
What you may notice instead depends on the juice and your body. A large load of fruit juice can raise blood sugar, especially in people with diabetes. Low food intake can leave some people hungry, tired, headachy, dizzy, or irritable. Juices rich in certain fruits and vegetables may also change bowel movements; removing much of the fiber found in whole produce can make stools less bulky.
The rebound is part of the story
When regular meals return, glycogen stores refill and bring water with them, so some of the quick scale loss can return. That does not mean the body has suddenly gained the same amount of fat. The more useful takeaway is that a cleanse’s visible short-term effects—fluid shifts, hunger, and altered digestion—are not evidence that toxins have been flushed out.
